The invention relates generally to rear axle assemblies for front wheel drive motor vehicles and more particularly to a rear axle assembly having two electromagnetic clutches and a bevel gear differential.
Traction control and vehicle stability systems are the subject of significant contemporary engineering study and development. Many utilize sophisticated software receiving data from, for example, four independent wheel speed sensors to control a transfer case clutch providing variable torque delivery and brake application in order to improve vehicle handling, braking and overall control.
Mechanical drive line components and electronic control systems are well represented in the prior art. For example, U.S. Pat. No. 5,407,024 teaches an adaptive drive system in which torque is constantly provided to the rear wheels of a vehicle and a modulating clutch within a transfer case automatically and incrementally provides torque to the front wheels when a speed difference between front and rear wheels in excess of a variable threshold is detected. Front wheel drive vehicles also incorporate unique adaptive torque delivery and stability control systems. In one front wheel drive system, a rear axle having a pair of clutches may be independently engaged to provide torque to the left and right rear wheels. This system is disclosed in U.S. Pat. No. 6,327,935.
It is apparent that additional and diverse mechanical drive line components and software incorporating control strategies for four wheel adaptive drive systems are both possible and desirable.
A rear axle assembly for a primary front wheel drive motor vehicle includes two electromagnetic clutches and a geared differential. A first electromagnetic clutch provides torque to the geared differential which, in turn, provides drive torque to two axles. The geared differential includes a second electromagnetic clutch operably disposed between the differential cage and the output shafts (axles). Activation of the first electromagnetic clutch provides controlled application of torque to the rear differential and activation of the second electromagnetic clutch progressively inhibits differentiation of the geared differential. The electromagnetic clutches may be actuated independently or together to provide three distinct operating modes: (1) only the first clutch actuated xe2x80x94operation as a four wheel drive vehicle with an open rear differential; (2) only the second clutch engagedxe2x80x94rear axle not driven but no speed differentiation between rear axles and (3) both clutches actuatedxe2x80x94operation as a four wheel drive vehicle with no rear axle differentiation. It will be appreciated that the foregoing descriptions refer to the fully energized or actuated states of the clutches solely for the purpose of illustration and explanation. Since the clutches are modulating clutches, proportional or partial engagement of the clutches is possible to achieve selected, modulated levels of torque transfer through the first clutch and partial inhibition of differentiation by the second clutch.
It is thus an object of the present invention to provide a rear axle assembly having two electromagnetic clutches.
It is a further object of the present invention to provide a rear axle assembly having two electromagnetic clutches and a geared differential.
It is a further object of the present invention to provide a rear axle assembly for front wheel drive motor vehicles having a first electromagnetic clutch which controllably provides torque to a geared differential having a second electromagnetic clutch which controllably inhibits differentiation of the differential.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same component, element or feature.